1. Field of the Invention
The present invention relates to a direct-vision/projection type liquid-crystal display.
2. Description of the Prior Art
Liquid-crystal display devices are advantageous in that they can be reduced in size, thickness, power consumption and other aspects, and are being increasingly used in OA instruments, AV instruments and other fields.
A liquid-crystal panel comprises two substrates formed with prerequisite electrodes, a liquid-crystal layer between the electrode forming faces of the two substrates disposed opposite to each other and a polarizing plate disposed on the outside of each of the substrates. Such a liquid-crystal panel forms a liquid-crystal module with various peripheral circuits thereon, such as a scan driver circuit for supply scan signals to the scan lines of the liquid-crystal panel, a data driver circuit for supplying pixel signals to the data lines of the liquid-crystal panel to cause a desired display at each pixel, an interface circuit for preparing original pixel signals, a control circuit for controlling the timing of panel input and other circuits.
The liquid-crystal display is classified into the direct-vision type and the projection type, depending on the combination of the liquid-crystal module with a source of light. The direct-vision type liquid-crystal display is used as a monitor display for TV or personal computer terminals by combining the liquid-crystal module with a surface light emission type back light or a surface light source member such as reflecting plate or the like. The projection type liquid-crystal display is used as a projector TV for enlarging and projecting a scene displayed on the liquid-crystal panel onto a screen or the like, by incorporating the liquid-crystal module into an optical system which may comprise a high-bright light source, mirrors and lenses.
Recently, there has been developed a projection type liquid-crystal display device which can be used in an overhead projector (OHP). Such a projection type liquid-crystal display uses a liquid-crystal module connected to a computer in place of OHP films which are generally used in overhead projectors. In such an OHP liquid-crystal display, the displayed scene can be handled through the computer's input unit such as a keyboard or the like, and does not require the time-consuming job of manually handling the OHP films. Particularly, if the liquid-crystal module is of an active matrix type, dynamic picture images can be displayed through input of R, G and B signals.
As described, the liquid-crystal display is classified into the direct-vision type and the projection type. The direct-vision type liquid-crystal display for TV or personal computer terminals requires a light source member such as back light or reflecting plate while the projection type liquid-crystal display does not require such a light source member since it uses a light source in the OHP. Unfortunately, the OHP liquid-crystal display raises a problem in that the liquid-crystal panel is heated by the OHP light source to reduce its display contrast. Therefore, the OHP liquid-crystal display must have means for overcoming the problem on heating.
Although the same liquid-crystal module having the same screen size can be used irrespectively of whether the liquid-crystal display is of direct-vision or projection type, the OHP liquid-crystal display may have to comprise the liquid-crystal module combined with the respective light source, depending on the application of the liquid-crystal display. Thus, the liquid-crystal display devices are disadvantageous in terms of flexibility and economy. In general, the monitor display is more frequently used to prepare data for a long time. On the other hand, the OHP liquid-crystal display is less frequently used to perform the presentation over a short time. Therefore, the OHP liquid-crystal display is lower in utilization and diffusion in spite of its high availability.